EXCHANGE 


I.  The  Equilibrium  in  Liquid  Mixtures  of 

Ammonia  and  Xylene 

II.  The  Molecular  Weight  of  Complex  So- 
dium Tellurides  in  Liquid  Ammonia 


BY 
EDWARD  H.  ZEITFUCHS 


A  DISSERTATION 


SUBMITTED  TO  THE  FACULTY  OF  CLARK  UNIVERSITY,  WORCESTER, 

MASS.,  IN  PARTIAL  FULFILLMENT  OF  THE  REQUIREMENTS  FOR 

THE  DEGREE  OF  DOCTOR  OF  PHILOSOPHY,  AND  ACCEPTED  ON 

THE  RECOMMENDATION  OF  CHARLES  A.  KRAUS 


CLARK  UNIVERSITY 

1 922 


EASTON,  PA.: 
ESCHENBACH   PRINTING  COMPANY 


L     The  Equilibrium  in  Liquid  Mixtures  of 
Ammonia  and  Xylene 

IL     The  Molecular  Weight  of  Complex  So- 
dium Tellurides  in  Liquid  Ammonia 


BY 
EDWARD  H.  ZEITFUCHS 


A  DISSERTATION 


SUBMITTED  TO  THE1  FACULTY  OF  CLARK  UNIVERSITY,  WORCESTER, 

MASS.,  IN  PARTIAL  FULFILLMENT  OF  THE  REQUIREMENTS  FOR 

THE  DEGREE  OF  DOCTOR  OF  PHILOSOPHY,  AND  ACCEPTED  ON 

THE  RECOMMENDATION  OF  CHARLES  A.  KRAUS 


CLARK  UNIVERSITY 

1922 


E ASTON,  PA.: 
ESCHENBACH    PRINTING  COMPANY 


I.     THE  EQUILIBRIUM  IN  LIQUID  MIXTURES   OF  AMMONIA 

AND  XYLENE 

Introduction 

Franklin  and  Kraus  have  observed  that  mixtures  of  ammonia  and  meta- 
xylene  have  an  upper  critical  end-point1  a  little  below  room  temperatures. 
Since  the  vapor-pressure  curves  of  only  a  few  such  systems  have  been 
studied  thus  far,2  it  appeared  worth  while  to  investigate  this  system  in 
some  detail.  In  as  much  as  the  vapor  pressure  of  xylene  is  low  compared 
with  that  of  ammonia,  the  total-pressure  curves  will  differ  little  from  the 
partial -pressure  curves. 

In  the  present  investigation  the  vapor  pressure  of  various  liquid  mix- 
tures has  been  determined  together  with  the  composition  of  the  liquid 
phases  of  the  monovariant  system.  The  latter  data  were  determined  in 
a  separate  series  of  experiments. 

The  critical  end-point  was  determined  in  a  special  experiment  by  direct 
observation  of  the  temperature  at  which  the  two  phases  become  identical. 
For  this  purpose  ammonia  and  wetaylene  were  sealed  in  a  heavy  walled 

1  This  is  sometimes  called  the  critical  point  of  solution.     Since  such  a  point  also 
occurs  in  the  diphase  system,  it  appears  preferable  to  designate  the  critical  point  of 
the  three-phase  system  as  critical  end-point,  as  has  been  suggested  by  Biichner. 

2  The  literature  relating  to  systems  of  this  type  has  been  collected  by  Biichner 
in  Part  2,  Vol.  II,  of  Roozeboom's  "Die  Heterogenen  Gleichgewichte  vom  Standpunkte 
der  Phasenlehre,"  and  detailed  references  may  accordingly  be  omitted  here. 


glass  tube  provided  with  an  electromagnetic  stirrer.  This  tube  was 
placed  in  a  bath,  contained  in  a  Dewar  tube,  the  temperature  of  which  was 
allowed  to  rise  slowly.  Keeping  the  mixture  vigorously  stirred,  the 
temperature  was  noted  at  which  the  two-phase  system  disappeared.  The 
mean  value  so  found  for  the  critical  end-point  was  14.7°. 

The  Vapor  Pressure  of  Liquid  Mixtures  of  Ammonia  and  Xylene 
Apparatus. — The  boiling  point  of  the  m^axylene  used  in  this  work 
was  found  to  be  close  to  139. 2 °t  the  value  given  in  Landolt-Bornstein's 
Tables  of  Physico-chemical  Constants  for  the  boiling  point  of  pure  m- 
xylene.  The  ammonia  was  drawn  from  a  container  in  which  it  had  been 
purified  by  the  method  given  by  Franklin  and  Kraus.3  The  arrangement 
of  the  apparatus  used  to  measure  the  total  pressure  of  the  vapor  of  mix- 
tures oHiquid  ammonia  and  liquid  xylene  is  shown  in  Fig.  1. 


Fig.  1.— The  apparatus  employed  in  determining  the  vapor  pressure  of  the 
mono  variant  system. 

All  parts  of  the  apparatus  which  were  under  pressure  were  constructed  of  metal, 
with  the  exception  of  the  mercury  column  R,  which  was  made  of  glass  tubing  of  1  mm. 
thickness  and  4  mm.  internal  diameter. 

The  liquid  mixture  was  contained  in  a  thin  walled  steel  tube  A  of  2.75  cm.  internal 
diameter  and  15  cm.  length.  This  tube  was  suspended  in  a  thermostat  containing 
kerosene  which  was  vigorously  stirred  and  whose  temperature  could  readily  be  controlled 
within  0.01°.  The  total  volume  of  the  liquid  mixture  in  Tube  A  varied  from  30  cc.  to 
70  cc.,  depending  on  the  composition.  A  brass  tube,  B,  12  mm.  o.  d.  by  9  mm.  i.  d.,  and 
20  cm.  long,  was  screwed  and  soldered  to  A.  A  steel  core,  having  a  diameter  of  8  mm. 
and  a  length  of  7.5  cm.  was  supported  in  the  bore  of  the  brass  tube  by  a  steel  piano  wire 
spring  of  No.  31  B.  and  S.  gage.  This  spring  was  fastened  to  the  brass  cap  C  which  was 

3  Franklin  and  Kraus,  Am.  Chem.  J.,  23,  284  (1900). 


5    * 

screwed  into  a  conical  seat  on  the  top  of  the  tube  A.  A  plunger  stirrer  was  suspended 
from  the  steel  core  by  means  of  a  heavy  steel  wire.  The  core  was  actuated  by  means  of  a 
solenoid  E  in  which  the  current  was  interrupted  once  per  second  by  means  of  a  motor 
driven  contact  breaker.  The  degree  of  stirring  could  be  regulated  by  adjusting  the  posi- 
tion of  the  solenoid  along  the  axis  of  the  brass  tube  and  by  resistance  placed  in  the  sole- 
noid circuit. 

Connection  was  made  with  the  manometer  R  by  means  of  a  mercury  reservoir  F 
of  thin  walled  steel  tubing  of  27  mm.  i.  d.  and  17.5  cm.  length.  To  its  ends  were  welded 
2  short  pieces  of  hexagonal  steel  which  were  machined  to  take  the  various  connections. 
Connection  with  the  mercury  column  was  made  through  the  valve  G,  The  column  had 
a  height  of  7.2  meters.  A  plug  carrying  an  insulated  platinum  contact  point  was  screwed 
into  the  top  of  F.  By  means  of  this  contact  point,  which  projected  into  a  small  opening 
near  the  top  of  the  mercury  reservoir,  the  level  of  the  mercury  could  be  maintained  at  a 
fixed  point  with  ease  and  precision.  The  position  of  the  platinum  point  was  transferred 
to  a  point  on  a  steel  tape  suspended  alongside  the  manometer  column.  Contact  of  the 
mercury  with  the  platinum  point  was  indicated  by  means  of  a  small  electric  lamp.  The 
amount  of  mercury  in  the  reservoir  was  regulated  by  means  of  the  mercury  displacement 
piston  H. 

Connection  between  the  tube  A,  containing  the  liquid  ammonia-liquid  xylene,  and 
the  mercury  reservoir  F,  was  made  by  means  of  a  small  bore  steel  tube  as  shown.  This 
capillary  steel  tube  connection  was  provided  with  a  valve  at  I,  by  means  of  which  the 
space  above  the  mercury  in  the  reservoir  and  the  tube  F  and  in  the  connecting  tube  could 
be  evacuated. 

The  ammonia  supply  was  contained  in  a  light  steel  cylinder  /.  The  steel  capillary 
tube  connecting  this  container  and  the  tube  A  could  be  evacuated  at  will  through  the 
valve  K.  The  desired  quantity  of  ammonia  was  distilled  from  the  container  J  into  the 
tube  A  on  opening  valves  L  and  M.  During  the  distillation,  the  temperature  of  the 
thermostat  was  maintained  near  8°,  while  the  ammonia  container  was  slightly  warmed 
by  resting  it  on  a  small  electrically  heated  plate.  The  quantity  of  ammonia,  which 
distilled  into  A ,  was  obtained  by  difference  in  the  weight  of  the  container  before  and  after 
the  distillation. 

The  description  of  the  method  of  determining  the  total  vapor  pressure 
of  a  mixture  of  liquid  xylene  and  liquid  ammonia  by  means  of  this  appa- 
ratus follows. 

Experimental  Method. — For  a  mixture  of  a  desired  composition, 
the  proper  amount  of  xylene  was  introduced  into  A  through  B  by  means 
of  a  weight  pipet  having  a  long  stem.  B  was  then  closed  by  Cap  C,  and 
A  was  evacuated.  The  desired  quantity  of  ammonia  was  next  distilled 
into  A  from  /  in  the  manner  described  above.  The  plunger  stirring  the 
liquid  in  A  was  then  set  in  motion  and  the  temperature  of  the  bath  was 
brought  to  the  value  desired. 

The  valve  G  connecting  the  mercury  column  and  the  mercury  reservoir 
was  then  cautiously  opened  and  the  column  allowed  to  adjust  itself  to 
the  pressure  in  the  apparatus,  after  which  mercury  was  forced  into  the 
reservoir  by  means  of  the  displacement  piston  H  until  contact  was  made 
with  the  platinum  point.  The  position  of  the  top  of  the  mercury  column 
was  read  on  a  graduated  steel  tape  suspended  with  its  zero  point  near  the 
top  of  the  column.  As  soon  as  the  position  of  the  meniscus  of  the  mercury 


column  became  constant,  two  readings  were  made  at  intervals  of  10  min- 
utes. The  height  of  the  column  of  mercury  was  given  by  the  difference 
in  reading  of  the  position  of  the  platinum  point  and  the  position  of  the  top 
of  the  mercury  column.  The  temperature  of  the  column  was  obtained 
from  thermometers  placed  at  120cm.  intervals  along  its  height.  The 
barometric  height  and  the  temperatures  were  read  for  every  measurement 
of  the  height  of  the  manometer  column,  and  the  temperature  of  the  room 
in  the  immediate  neighborhood  of  the  apparatus  was  noted.  The  tem- 
perature of  the  thermostat  was  then  changed  to  the  one  next  desired  and 
the  procedure  for  measuring  the  pressure,  as  just  described,  was  repeated. 

In  general,  for  a  given  composition,  the  run  was  started  at  8°  and  mea- 
surements of  the  pressure  were  made  at  8°,  10°,  12°,  14°,  15°,  17°  and  20°. 
In  some  cases,  for  a  mixture  of  given  composition,  the  pressure  measure- 
ments were  repeated  at  the  various  temperatures  as  the  temperature  was 
varied  from  8°  to  20°  and  back  from  20°  to  8°  by  the  intervals  given  above. 
The  agreement  of  the  measurements  in  any  such  case  was  found  to  lie 
well  within  the  limits  of  error  involved  in  other  parts  of  the  experimental 
work. 

Experimental  Results.— In  Table  I  are  given  in  detail  the  data  as 

obtained  for  a  complete  run  at  some  one  composition.     In  Table  II  are 

9 


30         40         50         60         70 
Mol  per  cent,  of  ammonia. 
Fig.  2. — Isotherms  of  the  mixtures. 


80 


90 


100 


given  the  values  of  temperature,  pressure,  and  mean  composition  for  all 
experiments  which  were  considered  satisfactory.  It  was  necessary  to 
correct  the  total  composition  of  the  liquid  ammonia-xylene  mixtures 
for  the  amount  of  ammonia  in  the  vapor  above  the  liquid  in  A  and  in  the 
tube  connecting  this  reservoir  with  F.  The  volume,  the  pressure  and  the 
temperature  of  the  vapor  rilling  this  space  were  in  all  cases  known,  and  from 
these  data  the  weight  of  ammonia  in  the  vapor  space  was  calculated, 
assuming  the  laws  of  perfect  gases  to  hold.  While  this  is  far  from  true 
for  ammonia4  at  these  high  pressures,  yet  the  error  introduced  was  neg- 
ligible, since  the  correction  for  ammonia  in  the  vapor  was  in  any  case 
small  compared  with  the  total  amount  of  ammonia  present.  This  cor- 
rection has  been  applied  to  the  compositions  given  in  Table  II. 

The  temperatures  given  in  Tables  I,  II  and  IV  are  subject  to  the  cor- 
rections indicated  in  Table  III,  which  were  obtained  by  comparing  the 
laboratory  thermometer  used  in  this  investigation  with  a  thermometer 
standardized  by  the  Reichsanstalt. 


Run  No.  6. 


TABUJ  I 

DETAILED  DATA  FOR  A  RUN 
Position  of  platinum  point  (transferred  to  steel  tape),  22.917  ft. 


Position 
of  top 
of  mercury 
Temperature        column 
of                   on  steel 
Thermostat0            tape 
0  C.                  Ft. 

Average 
Height  of    temp,  of 
mercury     mercury 
column       column 
Cm.             °C. 

Height  of 
mercury 
column     Barometer 
corrected,   corrected 
for  temp.0    for  temp. 
Cm.               Cm. 

Pressure  of 
mixed 
xylene-ammonia 
vapors 
Cm.                Atm. 

8 

20.375 

77.48 

23 

77.19 

72.89 

150.08 

1.975 

10 

20.167 

83.82 

25 

83.49 

72.92 

156.41 

2.058 

12      - 

19.962 

90.07 

25 

89.71 

72.98 

162.69 

2.141 

14 

19.750 

96.53 

26 

96.11 

72.97 

169.08 

2.224 

15 

19.641 

99.85 

26 

99.43 

•   72.97 

172.40 

2.268 

17 

19.416 

106.70 

26 

106.25 

72.98 

179.23 

2.358 

20 

19.078 

117.00 

26 

116.52 

72.99 

189.51 

2.493 

0  Temperature  subject  to  corrections  given  in  Table  III. 

b  Corrections  obtained   from   "Physikalische-Chemische   Tabellen"   by   Landolt- 
Bornstein. 

In  Fig.  2  the  pressures  given  in  Table  II  are  plotted  as  ordinates  against 
the  temperatures  as  abscissas.  The  horizontal  portions  of  the  isotherms 
represent  the  mean  composition  of  the  mixture  for  which  2  liquid  phases 
are  present.  The  end-points  of  the  horizontal  portions  give  the  compo- 
sition of  the  2  liquid  phases  in  equilibrium  with  each  other.  These  points, 
at  which  the  isotherms  become  horizontal,  can  be  estimated  only  roughly 
from  the  plots.  As  it  was  desirable  to  know  the  composition  of  the  2 
liquid  phases  somewhat  more  accurately,  a  separate  set  of  experiments 
was  carried  out  for  their  determination. 

4  Lange,  Z.  angew.   Chem.,   1903,  pp.  511-13. 


8 


TABLE  II 
VAPOR  PRESSURE  AND  MEAN  COMPOSITION  OP  MIXTURES  AT  DIFFERENT  TEMPERATURES 


*  111 
1^1 


m 


S.Z- 
11.S 

ofi£S 


Jill 


Run  4 

Run  5 

Run  6 

8 

4.64    31.0 

3.32     17.5 

1.97    9.5 

10 

4.89     30.9 

3.47     17.4 

2.06     9.5 

12 

5.15    30.9 

3.59     17.3 

2.14     9.5 

'  14 

5.43    30.8 

3.76     17.3 

2.22    9.4 

15 

5.56     30.8 

3.85     17.2 

2.27     9.4 

17 

5.86    30.8 

4.01     17.2 

2.36    9.3 

20 

6.30    30.7 

4.27     17.1 

2.49     9.3 

Run    8 

Run    9 

Run  11 

8 

2.46     12.0 

4.16    25.2 

4.87    35.2 

10 

2.57     11.9 

4.37    25.1 

5.14     35.1 

12 

2.67     11.9 

4.60    25.0 

5.43     35.0 

14 

2.79     11.8 

4.83     25.0 

5.73     35.0 

15 

2.85     11.8 

4.94    25.0 

5.88    34.9 

17 

2.97     11.8 

5.19    24.9 

6.20    34.8 

20 

3.15     11.7 

5.56    24.8 

6.70    34.8 

Run  12 

Run  13 

Run  14 

8 

5.01     38.1 

5.18    42.6 

5.29    46.1 

10 

5.31     38.1 

5.49    42.5 

12 

5.61     38.0 

5.81     42.5 

14 

5.92    37.9 

6.14    42.3 

6.30    46.1 

15 

6.10    37.9 

6.31     42.2 

6.46    45.9 

17 

6.40    38.0 

6.68    42.4 

20 

6.93    37.9 

7.31     42.2 

Run  15 

Run  16 

Run  17 

8 

5.42    50.1 

5.43     54.2 

5.48    64.6 

10 

5.70    50.2 

Run  18 

Run  19 

Run  20 

8 

5.48    78.1 

5.50    86.5 

5.51     89.1 

10 

5.86    78.1 

5.87    86.5 

5.88    89.1 

12 

6.25     78.1 

6.28    86.6 

6.29    89. 

14 

6.66    78.1 

6.70    86.6 

6.70    89. 

15 

6.89    78.0 

6.91     86.5 

6.93     89. 

17 

7.34    78.0 

7.36    86.4 

7.39    89. 

20 

8.06    78.0 

8.10    86.4 

8.10    89. 

Run  21 

Run  22 

Run  23 

8 

5.50    91.2 

5.54     96.4 

5.62     Pure  ammonia 

10 

5.86    91.1 

5.92    96.3 

6  .  02     Pure  ammonia 

12 

6.28    91.1 

6.33    96.3 

6.44     Pure  ammonia 

14. 

6.70    91.0 

6.79    96.3 

6  .  90     Pure  ammonia 

15 

6.92    91.0 

6.98    96.3 

7.11     Pure  ammonia 

17 

7.39    90.9 

7.46    96.3 

7  .  60     Pure  ammonia 

20 

8.13     90.8 

8.19    96.3 

8.39     Pure  ammonia 

Run 

24 

Run  26 

Run  28 

8 

5 

.60 

98 

.7 

5 

.50 

95. 

1 

5.37 

50 

.2 

10 

6 

.00 

98, 

7 

5 

.88 

95. 

0 

.  . 

, 

p 

12 

6 

.41 

98. 

7 

6 

.30 

95. 

0 

, 

' 

. 

14 

6 

.86 

98. 

7 

6 

.73 

95. 

0 

•t 

. 

. 

15 

7 

.09 

98. 

7 

6 

.95 

95. 

0 

. 

. 

17 

7 

.56 

98. 

7 

7 

.41 

95. 

0 

.  . 

, 

20 

8 

.33 

98. 

7 

8 

.18 

95. 

0 

e 

p 

x 

Run 

30 

Run  31 

Run  32 

8 

5 

.12 

41. 

3 

5 

.39 

52. 

3 

5.47 

60 

.8 

10 

5 

.42 

41. 

3 

5 

.74 

52. 

3 

5.84 

60 

.8 

12 

5 

,71 

41. 

6 

6 

.09 

52. 

1 

6.22 

60 

.7 

14 

6 

.06 

41. 

1 

6 

.46 

52. 

1 

6.61 

60 

.7 

15 

6 

.24 

41. 

1 

6 

.65 

52. 

1 

6.82 

60 

.7 

17 

6 

58 

41. 

1 

7 

.05 

51. 

9 

7.24 

60 

.6 

20 

7, 

13 

40. 

9 

7 

.68 

51. 

9 

7.91 

60 

.5 

Run 

33 

Run  34 

Run 

35 

8 

5 

,49 

67. 

5 

5 

.50 

73. 

4 

5.53 

80 

.2 

10 

5 

.86 

67. 

4 

5 

.88 

73. 

4 

. 

. 

12 

6 

.26 

67. 

4 

6 

.28 

73. 

4 

.  .. 

. 

14 

6 

.67 

67. 

4 

6 

.69 

73. 

4 

15 

6 

.88 

67. 

3 

6 

.91 

73. 

4 

. 

17 

7. 

31 

67. 

3 

7 

.35 

73. 

4 

p- 

, 

t 

20 

8 

01 

67. 

3 

8 

.06 

73. 

4 

a  t 

t 

Run 

36 

Run 

37 

8 

5 

,53 

81. 

8 

5 

.51 

83. 

4 

10 

5 

.89 

81. 

8 

5.89 

83. 

4 

12 

6 

30 

81. 

8 

6 

.28 

83. 

4 

14 

6 

,72 

81. 

8 

6 

.70 

83. 

4 

15 

6 

94 

81. 

8 

6 

.92 

83. 

4 

17 

7, 

39 

81. 

8 

7 

.37 

83. 

4 

20 

8, 

12 

81. 

8 

8 

.10 

83. 

4 

°A11  temperatures  given  in  Table  II  are  subject  to  the  corrections  given  in  Table  III. 

TABLE  III 
THERMOMETER  CORRECTIONS 

Reading  on          Reading  on  Reading  on         Reading  on   . 

laboratory  Reichsanstalt's  laboratory  Reichsanstalt's 

thermometer         thermometer  thermometer  thermometer 
°C.                           °C.                                       °C.  °C. 

8  7.83  15  14.79 

10  9.82  17  16.79 

12  11.81  20  19.80 

14  13.79 

Composition  of  the  Liquid  Phases 

Apparatus. — In  Fig.  3  is  shown  the  apparatus  by  means  of  which 
the  composition  of  the  2  liquid  phases  was  determined.  In  a  preliminary 
experiment,  the  relative  volumes  of  the  2  phases  were  determined  by  ob- 
servations made  on  mixtures  contained  in  a  glass  tube  of  uniform  diameter. 
The  mean  composition  of  the  liquid  mixture  used  in  this  preliminary  ex- 
periment corresponded  to  that  at  the  critical  point,  K,  which  was  esti- 


10 


mated  from  the  plot  shown  in  Fig.  2.  The  relative  volumes  of  the  2  layers 
in  the  glass  tube  changed  only  a  few  per  cent,  for  a  temperature  change  from 
8°  to  14.7°,  the  temperature  of  the  critical  end-point.  With  this  knowl- 
edge of  the  volumes  occupied  by  the  2  phases  of  a  mixture  of  known  mean 
composition,  the  apparatus  shown  in  Fig.  3  was  designed.  The  volumes 
of  the  chambers  A,  B  and  C  were  so  proportioned  that,  when  in  an  upright 
position,  the  surface  separating  the  two  liquid  layers  should  always  come 
within  the  mid  section  B  for  temperatures  from  8°  to  14°. 

Procedure. — The  procedure  adopted  in  mak- 
ing a  determination  of  the  composition  of  the 
two  liquid  phases  at  a  given  temperature  is  as 
follows.  The  desired  quantity  of  xylene  was  run 
into  Chamber  C  from  a  weight  pipet.  The  two 
parts  of  the  apparatus  were  then  screwed  together 
at  the  conical  joint  D,  and  the  whole  was  then 
placed  in  the  thermostat  in  an  upright  position 
with  Chamber  C  at  the  bottom.  The  outlet  valve 
E  was  connected  by  means  of  a  steel  tube  to  the 
valve  K,  shown  in  Fig.  1.  After  evacuation,  the 
desired  quantity  of  ammonia  was  distilled  into  the 
apparatus.  The  quantity  of  ammonia  introduced 
was  obtained  by  difference  in  the  weight  of  the 
container.  Valve  E  was  then  closed  and  the  whole 
apparatus  was  shaken  at  brief  intervals,  for  a 
period  of  half  an  hour.  The  apparatus  was  then 
allowed  to  remain^at  rest  for  10  or  15  minutes 
to  allow  thorough  separation  of  the  layers.  Valve 
F  was  then  closed,  thus  sealing  a  portion  of  the 
Fig.  3.— Apparatus  em-  lower,  heavier  layer  in  Chamber  C.  A  valve  shown 
ployed  in  determining  the  at  £  was  next  opened  to  allow  for  the  expansion 

°f  the  Hquid  due  t0  temPerature  rise  when  the 
apparatxis  was  removed  from  the  bath.  The 
valve  H  was  then  closed,  sealing  a  portion  of  the  upper,  lighter  layer 
in  the  chamber  A.  The  apparatus  was  then  removed  from  the  bath, 
the  portion  in  the  mid  section  B  was  discarded  through  valve  E,  after  which 
the  two  parts  of  the  apparatus  were  separated  at  the  conical  joint  D. 
Each  portion  of  the  apparatus  was  weighed.  The  ammonia  in  A  and  C 
was  determined  by  running  these  portions  into  known  quantities  of  stand- 
ard sulfuric  acid  and  titrating  back  with  sodium  hydroxide.  The  empty 
parts  of  the  apparatus  were  then  again  weighed,  and  the  weight 
of  the  sample  of  the  liquid  layer  was  obtained  by  difference. 

Experimental  Results.— The  following  are  the  data  in  detail  as  ob- 
tained in  one  of  these  determinations. 


it 

11 

EXPERIMENT  6  AT  12° 

Wt.  of  part  of  apparatus  containing  upper  portion  of  xylene- 

ammonia  mixture 481 . 630  g. 

Wt.  of  apparatus  empty 480.326  g. 

Wt.  of  sample  of  xylene-ammonia 1 .304  g. 

Vol.  of  0.953  N  H2SO4  neutralized  by  xylene-ammonia  sample .  49 . 89  cc. 

Ammonia  in  sample 0.04760  mols  =o  0.810  g. 

Xylene  in  sample 0.494  g.  o  0.00467  mols 

Mol  per  cent,   of  ammonia 90 . 3 

Wt.  of  part  of  apparatus  containing  lower  portion  of  xylene- 
ammonia  mixture 429 . 648  g. 

Wt.  of  apparatus  empty 427 . 585  g. 

Wt.  of  sample  of  xylene-ammonia 2 . 063  g. 

Vol.  of  0.953  N  H2SO4  neutralized  by  xylene-ammonia  sample .  27 . 27  cc. 

Ammonia  in  sample 0.0260  mols  =c=  0.442  g. 

Xylene  in  sample 1 .621  g.  =s=  0.0153  mols 

Mol  per  cent,  of  ammonia 63 . 0 

In  Table  IV  are  given  the  results  of  the  determinations  of  the  compo- 
sition at  8°,  10°,  12°  and  14°.  In  Fig.  2,  these  values  of  the  composition 
are  represented  on  their  respective  isotherms  as  points  surrounded  with 
circles. 

TABLE  IV 

COMPOSITION  OF  THE  Two  LIQUID  PHASES  AT  DIFFERENT  TEMPERATURES 

NH,  NH, 

in  in 

upper  lower 

Run           Temp.           layer  layer 

°C.             %  % 

12  8          93.7          56.5 

13  8          93.4          56.8 

14  8          93.4          56.8 

3  10  92.0  60.5 

4  10  92  4  60.3 

5  10  91.7  59.5 

15  10  92.3  60.4 

6  12  90.3  63.0 

7  12  90.3  64.0 
11  12  90.9  64.3 

8  14  87.2 

9  14  87.2  71.8 
10  14  88.1  71.8 

Av.  8  93.6  56.7 

Av.  10  92.2  60.4 

Av.  12  90.5  63.8 

Av.  14  87.5  71.8 

The  composition  of  the  two  liquid  phases  was  determined  at  the  boiling 
point  of  liquid  ammonia  at  atmospheric  pressure  by  means  of  another 
apparatus.  In  this  experiment  a  known  weight  of  xylene  was  run  into 
a  glass  tube  which  was  provided  with  a  stirrer  and  which  was  immersed 


12 

in  liquid  ammonia  contained  in  a  Dewar  flask.  After  exhausting,  ammonia 
was  distilled  into  the  tube  until  2  phases  appeared,  the  liquid  being  vig- 
orously stirred  in  the  meantime.  The  amount  of  ammonia  distilled  over 
was  determined  by  the  change  in  the  weight  of  the  supply  container.  By 
this  means  the  composition  of  the  solution  rich  in  xylene  was  determined. 

To  obtain  the  composition  of  the  phase  rich  in  ammonia,  the  above 
procedure  was  repeated,  but  with  a  small  amount  of  xylene  present  at  the 
beginning.  The  point  was  noted  at  which  the  xylene  phase  disappeared. 
From  the  known  weights  of  xylene  and  ammonia  present,  the  composition 
of  the  phase  rich  in  ammonia  was  thus  found. 

It  was  difficult  to  determine  accurately  the  appearance  of  a  second 
phase  or  the  disappearance  of  the  first  phase,  and  the  results  obtained  in 
this  part  of  the  work  may  be  in  error  by  several  per  cent.  The  values 
found  were  10. 0  mol  per  cent,  of  ammonia  for  the  phase  rich  in  xylene,  and 
0.56  mol  per  cent,  of  xylene  in  the  phase  rich  in  ammonia. 

The  broken  line  curve  shown  in  Fig.  2,  passing  through  the  circles  on  the 
isotherms,  represents  the  composition  of  the  liquid  phases  in  equilibrium 
with  each  other 

Discussion 

The  form  of  the  pressure-concentration  isotherms  shown  in  Fig.  2 
places  the  system  ammonia :  wetaylene  among  Biichner's  first  type,5 
in  which  the  pressure  of  the  3-phase  system  lies  intermediate  between 
that  of  the  pure  components.  In  general,  it  has  been  found  that  liquid 
pairs  having  relatively  high  boiling  points  fall  within  this  class,  while 
liquid  pairs  whose  boiling  points  are  comparable  fall  within  the  class  in 
which  the  pressure  of  the  3-phase  system  is  higher  than  that  of  the 
components. 

Biichner  has  found,  as  a  result  of  an  examination  of  a  large  number  of 
systems  of  this  type,  that  a  temperature  difference  of  at  least  100°  must 
exist  between  the  boiling  points  of  the  two  compounds,  in  order  that  they 
should  fall  within  this  class.  There  are,  however,  several  exceptions  to 
this  rule.  Biichner  finds  also  that  the  ratio  of  the  critical  temperatures 
of  the  pairs  which  belong  to  this  group  has  a  value  equal  to,  or  greater  than, 
1.4.  The  system  ammonia: xylene  fulfils  both  these  conditions,  the  dif- 
ference in  the  boiling  points  being  172.7°,  while  the  ratio  of  the  critical 
temperatures  is  1.41. 

Considering  the  isotherms,  the  behavior  of  the  mixtures  of  ammonia  and 
xylene  is  such  as  might  be  expected.  At  temperatures  below  the  critical 
end-point,  the  isotherms  appear  very  much  flattened  at  compositions  ap- 
proaching those  of  the  2  liquid  phases.  So,  also,  above  the  critical  point, 
the  isotherms  at  compositions  in  the  neighborhood  of  the  critical  compo- 
sition are  comparatively  flat.  This  system  differs  from  other  systems 
6  Ref.  2,  p.  34. 


13    ' 

most  largely,  perhaps,  in  that  the  critical  region  is  relatively  contracted 
on  one  side  of  the  figure.  Whereas  in  many  cases  the  critical  composition 
lies  in  the  neighborhood  of  50%  of  the  2  components,  in  this  system  the 
critical  composition  has  a  value  of  approximately  82  mol  per  cent,  of  am- 
monia. As  may  be  seen  from  Fig.  2,  the  composition  of  the  2  liquid 
phases  diverges  largely  at  lower  temperatures,  so  that  at  the  boiling  point 
of  liquid  ammonia  the  phase  rich  in  xylene  contains  only  10  mol  per  cent, 
of  ammonia  while  that  rich  in  ammonia  contains  only  0.56  mol  per  cent, 
of  xylene.  From  the  form  of  the  curve,  it  may  be  inferred  that  this 
system  will  not  exhibit  a  lower  critical  end-point.  In  any  case,  the  freezing 
point  of  ammonia  is  reached  at  a  temperature  of  approximately  —76°, 
and  a  solid  phase  thus  intervenes.  It  is  doubtful,  however,  whether  this 
system  may  be  looked  upon  as  having  a  lower  critical  end-point,  even  in 
the  metastable  regions. 

Very  striking  is  the  large  deviation  of  the  pressure  curves,  which  in 
this  case  are  practically  identical  with  the  partial  pressure  curves  of  am- 
monia, from  Raoult's  law  at  low  concentrations  of  xylene.  It  is  theo- 
retically necessary  that,  at  the  ammonia  axis,  the  pressure  curves  shall 
become  tangent  to  the  straight  line  joining  the  pressure  of  this  component 
with  the  origin  on  the  opposite  side  of  the  diagram.  It  is  evident,  from 
the  form  of  the  curves,  that  the  deviations  from  Raoult's  law  must  be  large 
even  at  relatively  low  concentrations.  There  is  thus  an  intimate  relation 
between  the  deviations  from  Raoult's  law,  that  is  to  say,  the  deviations  of 
a  real  system  from  that  of  an  ideal  one,  and  the  appearance  of  new  phases 
in  the  system.  Our  knowledge  of  the  fundamental  causes  leading  to  a 
separation  of  a  system  into  2  phases  is  as  yet  too  limited  to  enable  us  to 
interpret  the  phenomena  observed,  but  it  is  clear,  even  now,  that  the  ap- 
pearance of  new  phases  involves  appreciable  deviations  from  the  laws  of 
ideal  systems.  The  greater  the  difference  in  the  physical  properties  and 
constitution  of  the  components  in  a  mixture,  the  lower  is  the  concentration 
at  which  the  deviations  from  ideal  systems  reach  appreciable  values; 
and  the  lower  is  the  concentration  of  the  second  component  at  which  a 
new  phase  may  appear.  This  is  strikingly  illustrated  in  the  case  of  the 
system  sodium :  liquid  ammonia,  in  which  a  critical  phase  appears  having 
a  composition  of  approximately  97  mol  per  cent,  of  ammonia.6  This  corre- 
sponds to  a  concentration  a  little  above  normal. 

It  follows  from  the  theory  of  liquid  mixtures  that  the  isotherms  in  the 
homogeneous  regions  are  two  branches  of  a  continuous  curve,  which  rep- 
resents the  pressure  of  a  homogeneous  system  over  the  complete  concen- 
tration range.  Between  the  compositions  of  the  2  liquid  phases,  however, 
the  homogeneous  states  are  metastable  and  unstable,  and  are  therefore 
6  Kraus,  /.  Am.  Chem.  Soc.,  29,  1557  (1907).  Ruff  and  Zedner,  Ber.,  41,  1948 
(1908). 


14 

only  realizable  in  part,  excepting  on  the  critical  isotherm.  It  has  not 
been  found  possible  thus  far  to  evolve  a  theory  of  mixtures  sufficiently 
general  in  nature  to  include  the  case  of  systems  in  which  one  or  both  of  the 
components  are  abnormal  liquids.  It  is  clear,  however,  that  the  theoretical 
isotherm  must  exhibit  a  maximum  and  a  minimum  in  this  region.  In 
the  figure,  the  broken  line  connecting  the  points  B  and  C  indicates  such 
a  form  of  the  curve.  It  may  be  inferred,  since  the  isotherms  immediately 
above  the  critical  end-point  as  well  as  in  the  homogeneous  regions  adjacent 
to  the  3-phase  equilibrium  are  comparatively  flat,  that  the  theoretical 
isotherm  throughout  the  metastable  and  unstable  regions  will  be  com- 
paratively flat. 

Summary 

1.  The  total  vapor  pressure  of  liquid  mixtures  of  ammonia  and  meta- 
xylene  has  been  determined  for  the  entire  range  of  compositions  at  tem- 
peratures of  8°,  10°,  12°,  14°,  15°,  17°  and  20°.     Mixtures  of  liquid  am- 
monia and  wetaxylene  exhibit  a  critical  end-point  at  14.7°  at  a  pressure 
of  6.85  atmospheres  and  a  composition  of  81.4  mol  per  cent,  of  ammonia. 

2.  The  composition  of  the  liquid  phases  in  equilibrium  with  each  other 
in  the  3-phase  system  has  been  determined  at  the  temperatures  given 
above  and  at  —33 . 5°.     At  lower  temperatures  the  percentage  of  ammonia 
in  the  phase  rich  in  xylene  decreases  very  markedly  with  the  temperature. 

3.  The  significance  of  the  results  obtained  is  briefly  discussed. 


II.    THE  MOLECULAR  WEIGHT  OF  THE  SODIUM-TELLURIUM 
COMPLEX  IN  LIQUID  AMMONIA  AS  DERIVED  FROM  VAPOR- 
PRESSURE  MEASUREMENTS 

Introduction 

As  a  result  of  the  investigations  of  Kraus,1  Posnjak,  Smyth,2  and 
Kraus  and  Chiu,3  the  atomic  proportions  in  which  sodium  appears  com- 
bined with  lead  and  with  tellurium  in  liquid  ammonia  solution  have  been 
definitely  established. 

1  Kraus,  /.  Am.  Chem.  Soc.  29,  1556  (1907). 

2  Posnjak,  see  Smyth,  ibid.,  39,  1299  (1917). 

3  Kraus  and  Chiu,  ibid.,  44,  1999,  1922. 


15 

/* 

In  equilibrium  with  metallic  lead,  one  atom  of  sodium  appears  combined 
with  2.25  atoms  of  lead  in  ammonia  solution.  Smyth  has  suggested  that 
in  solution  several  lead  compounds  containing  various  amounts  of  lead 
exist  in  equilibrium  with  each  other.  Since  the  ratio  of  lead  to  sodium 
appears  to  be  independent  of  concentration,  the  equilibrium  among  the 
complexes  is  not  displaced  by  concentration  change. 

In  the  case  of  solutions  containing  sodium  and  tellurium,  the  ratio  of 
tellurium  to  sodium,  varies  as  a  function  of  the  concentration  (of  sodium) , 
as  was  shown  by  Allison,4  Power5  and  Kraus  and  Chiu.3  At  a  concentra- 
tion in  the  neighborhood  of  2  N,  the  ratio  of  tellurium  to  sodium  has  a  value 
of  approximately  2.02,  and  this  ratio  remains  very  nearly  constant  to  con- 
centrations as  low  as  0.5  N,  after  which  it  begins  to  decrease  as  the  con- 
centration decreases. 

Kraus  and  Chiu  have  investigated  the  system,  sodium-tellurium-am- 
monia, in  some  detail  and  have  established  the  fact  that  the  reaction  be- 
tween sodium  and  tellurium  takes  place  in  several  stages.  The  first  prod- 
uct of  the  reaction  is  the  normal  telluride,  Na2Te,  which  compound  further 
reacts  with  tellurium  to  form  a  solution  the  composition  of  which  corre- 
sponds to  the  formula  Na2Te2.  The  composition  of  the  solution  remains 
fixed  so  long  as  the  normal  telluride  is  present.6  In  the  presence  of  the  free 
metal  (tellurium)  the  telluride  Na2Te2  reacts  further  with  tellurium  to  form 
a  telluride  or  a  mixture  of  tellurides  containing  larger  amounts  of  this  ele- 
ment. As  has  already  been  noted,  the  ratio  of  tellurium  to  sodium  in  a 
solution  in  equilibrium  with  free  metallic  tellurium  varies  with  the  concen- 
tration. 

The  question  naturally  arises :  What  is  the  nature  of  the  solutions  of  the 
complex  telluride?  It  has  been  shown  that,  in  solutions  containing  the 
compounds  of  sodium  and  lead  and  sodium  and  antimony,  the  less  electro- 
negative element  functions  as  anion,  since  it  may  be  precipitated  in  the  free 
state  on  the  anode  by  electrolysis.  In  the  case  of  a  normal  salt,  such  as  the 
telluride,  Na2Te,  there  is  every  reason  for  believing  that  in  solution  the 
tellurium  is  present  as  a  normal  telluride  ion  carrying  2  negative  charges. 
When,  however,  the  normal  telluride  reacts  further  with  tellurium,  the 
question  arises:  Is  a  complex  anion  formed,  consisting  of  the  original 
telluride  ion  associated  with  other  atoms  of  tellurium ;  or,  conceivably,  does 
the  valence  of  the  tellurium  ion  change?  In  the  former  case  the  formula 
of  the  first  complex  telluride  would  be  Na2Te2,  while  in  the  latter  case  its 

4  V.  C.  Allison,  Thesis,  Clark  University,  1916. 

6  F.  W.  Power,  ibid.,  Clark  University,  1917. 

6  At  low  concentrations,  the  ratio  of  tellurium  to  sodium  in  the  solution  would, 
of  course,  diminish  if  the  solubility  of  the  normal  telluride,  NaaTe,  were  appreciable. 
The  solubility  of  the  normal  telluride,  however,  is  extremely  low,  for  which  reason,  at 
higher  concentrations,  this  ratio  in  solutions  which  are  in  equilibrium  with  the  normal 
telluride  remains  fixed. 


16 

formula  would  be  NaTe.  That  is,  we  should  in  one"  case  have  the  complex 
telluride  ion  Te — Te  with  2  negative  charges,  and  in  the  second  case  the 
ion  Te~  with  a  single  negative  charge.  It  is  by  no  means  obvious  that  the 
latter  process  may  not  occur. .  So  far,  we  have  so  little  information  regard- 
ing complex  compounds. of  this  type  that  it  would  be  unsafe  to  draw  any 
definite  conclusion  without  further  data. 

If  the  complex  telluride  ion  carries  2  charges,  then  obviously  the  formula 
of  the  compound  will  be  Na2Te  Te*.  By  means  of  molecular  weight 
determinations  it  should  be  possible  to  distinguish  between  the  alternative 
possibilities  suggested  above.  According  to  Franklin  and  Kraus,7  the 
molecular  weight  of  salts  in  ammonia  solution  at  ordinary  concentrations 
is  practically  normal,  which  corresponds  roughly  with  their  electrical  prop- 
erties, since  their  ionization  at  ordinary  concentrations  is  comparatively 
low.  It  might  be  expected,  therefore,  that  the  molecular  weight  of  the 
complex  tellurides  could  be  determined  in  ammonia  solution.  As  Kraus 
has  already  pointed  out,8  the  only  readily  available  method  for  determining 
molecular  weights  in  ammonia  solution  is  that  of  determining  the  vapor- 
pressure  change  due  to  the  solute.  In  the  following  investigation,  there- 
fore, this  method  has  been  adopted  for  the  purpose  of  determining  the 
molecular  complexity  of  the  complex  tellurides  in  ammonia  solution. 

Apparatus  and  Experimental  Method 

The  experimental  method  employed  in  this  investigation  is  essentially 
the  same  as  that  employed  by  Kraus  in  determining  the  molecular  weight 
of  sodium  in  liquid  ammonia  solution.  The  apparatus  employed  consists 
essentially  of  4  parts :  first,  a  thermostat,  by  means  of  which  the  tempera- 
ture may  be  maintained  constant  to  0.001°  or  better;  second,  a  device  for 
measuring  accurately  pressure  differences  of  the  order  of  magnitude  of  1.0 
mm.  of  mercury;  third,  the  containing  vessels  for  the  solutions  and  the 
solvent,  together  with  means  for  agitating  the  liquids;  and  fourth,  a  means 
of  introducing  known  amounts  of  the  metals  and  of  ammonia  into  the  con- 
taining vessel. 

The  Thermostat. — It  is  essential  that  the  temperature  be  kept  below  that  of  the 
surroundings ;  otherwise  the  solvent  will  distil  into  the  cooler  parts  of  the  apparatus. 
Cooling  was  accomplished  by  allowing  cold  tap  water  to  flow  continuously  through 
a  3-meter  length  of  copper  tubing  of  5  mm.  internal  diameter.  This  tube  was  immersed 
in  the  thermostat  liquid,  as  will  be  described  more  in  particular  below.. 

The  desired  temperature  was  maintained  by  means  of  a  steel  encased  mercury 
thermo-regulator  and  an  electrically  heated  coil  of  heavy  resistance  wire.  The  copper 
cooling  tube,  in  the  form  of  a  flat  spiral,  and  the  heating  element,  of  bare  Nichrome  wire 
wound  in  spiral  form,  were  placed  concentrically  around  the  shaft  of  the  stirrer  and  just 
above  a  cylindrical  tube  in  which  the  stirrer  revolved.  It  was  found  necessary  to  main- 
tain very  vigorous  stirring.  The  thermostat  contained  approximately  110  liters  of 

7  Franklin  and  Kraus,  Am.  Chem.  /.,  20,  837  (1898). 

8  Kraus,  J.  Am.  Chem.  Soc.,  30,  1197  (1908). 


17,, 

kerosene.  Even  though  the  thermostat  seemed  to  be  regulating  well  within  0.001°, 
it  was  found  impossible  to  obtain  consistent  readings  of  the  pressure.  Apparently,  the 
tubes  containing  the  pure  ammonia  and  the  ammonia  solution  of  the  telluride  were 
subject  to  temperature  fluctuations  due,  in  part  at  least,  to  incomplete  mixing  of  the 
liquid  in  the  thermostat.  Increasing  the  stirring  through  the  introduction  of  additional 
stirrers  did  not  prove  effective. 

In  order  to  overcome  this  difficulty,  a  square  box  C,  of  which  a  section  is  shown  in 
Fig.  1,  11.5  x  30.5  cm.  internal  dimensions,  constructed  of  1cm.  asbestos  board,  and 
provided  with  a  chimney  projecting  6  mm.  above  the  liquid  in  the  thermostat,  was 
then  placed  around  the  con  tamers  A  and  B  as  shown  in  the  figure.  Ali  the  joints  in  this 


Fig.  1.— Apparatus  employed  in  determining  the  vapor-pressure  lowering  due  to 
complex  tellurides  dissolved  in  liquid  ammonia. 

box  were  made  tight  so  that  no  liquid  passed  in  or  out.  The  liquid  in  this  box  was 
stirred  vigorously  by  means  of  a  small  propeller,  driven  from  the  same  motor  as  that 
which  drove  the  large  stirrer  in  the  main  thermostat.  With  this  arrangement  it  was 
found  possible  to  obtain  reasonably  consistent  readings.  The  box  served  to  integrate 
the  temperature  fluctuations  in  the  main  thermostat  in  the  immediate  neighborhood 
of  the  containers  A  and  B. 

The  Containers. — The  general  scheme  of  the  apparatus  is  shown  in  Fig.  1.  A 
and  B  are  the  containers.  These  are  identical  in  every  respect  except  that  B  is  fitted 
with  a  means,  shown  at  D,  for  introducing  the  sodium  into  the  ammonia.  The  tube  B 
is  shown  in  section.  The  containers  are  constructed  of  steel,  and  are  lined  with  glass 


18 

nearly  up  to  the  hexagonal  connecting  piece  to  which  H  is  attached.  The  steel  shell  has 
a  thickness  of  approximately  0.8  mm.  and  the  glass  lining  is  of  approximately  the  same 
thickness.  The  upper  part  of  B,  to  which  the  movable  plunger  D  is  attached,  is  con- 
structed of  2.5cm.  hexagonal  steel  stock.  This  hexagonal  portion  is  provided  with  2 
outlets.  One  of  these  outlets,  into  which  H  is  screwed,  leads  to  the  pressure-measuring 
device;  the  other  is  fitted  with  a  valve  similar  to  /,  shown  attached  to  A  in  the  figure. 
Each  container  consists  of  2  parts  which  are  screwed  together,  a  tight  joint  being  ob- 
tained by  means  of  the  conical  seat  shown  at  G.  The  upper  portion  of  A ,  as  of  B,  con- 
sists of  the  short  22mm.  hexagonal  steel  section  /  to  which  is  screwed  and  soldered  the 
brass  tube  K.  This  tube  has  an  internal  diameter  of  1  cm.  and  a  wall  thickness  of  1.5 
mm.  At  the  top,  K  is  provided  with  a  conical  seat  fitting  into  the  brass  cap  L.  M 
is  a  piece  of  steel  rod  of  8  mm.  diameter  and  9  cm.  in  length.  This  rod  is  suspended  from 
the  cap  L  by  means  of  a  spring  of  steel  piano  wire.  From  the  lower  end  of  M  is  sus- 
pended the  glass  stirrer  O  by  means  of  a  length  of  platinum-iridium  wire.  The  stirrer  O 
is  made  by  wrapping  a  glass  rod  of  3  mm.  diameter  spirally  around  another  rod  of 
approximately  the  same  size.  The  stirrer  system  is  actuated  by  means  of  the  solenoids 
PP,  the  current  in  which  is  interrupted  at  regular  intervals  by  means  of  a  motor-driven 
contact  device. 

The  means  for  adding  the  sodium  is  shown  at  D.  The  sodium  is  contained 
in  a  small  glass  capsule  E,  into  which  it  is  introduced  by  a  method  similar  to  that 
described  by  Kraus.8  B  is  provided  with  the  lugs  LL.  The  capsule  rests  on  the 
lower  lug,  while  the  upper  lug  with  the  plunger  D  serves  to  hold  the  capsule  in 
position.  The  capsule  E  is  placed  in  position  just  before  the  2  parts  of  B  are  screwed 
together.  At  any  desired  time  subsequently,  it  may  be  broken  and  allowed  to  drop 
to  the  bottom  of  the  container  below  by  simply  forcing  the  plunger  D  inward  against 
the  capsule.  The  valve  /  on  Container  A  and  an  identical  one  on  B  are  used  during  the 
evacuation  of  the  system,  and  the  introduction  and  the  removal  of  ammonia. 

The  Tensimeter. — The  tensimeter  consists  essentially  of  the  displacement  piston 
S  and  2  glass  tubes  Q  and  R,  provided  with  platinum  contacts  T  and  U  ground  to 
needle  points.  By  means  of  the  displacement  piston  5,  mercury  may  be  transferred 
from  the  cylinder  V  into  the  tubes  Q  and  R.  For  differences  in  pressure  of  less  than  2  cm. 
of  mercury,  use  is  made  of  the  2  contact  points  at  the  lower  ends  of  T  and  U,  as  will  be 
explained  below.  Tube  B,  containing  the  solution,  is  connected  to  R  containing  the 
point  situated  at  the  higher  level.  A  is  connected  to  the  tube  Q.  The  connecting  tubes 
leading  from  the  containers  to  Q  and  R  are  arranged  as  follows.  ZZ  are  flexible  copper 
tubes  of  5  mm.  internal  diameter  soldered  to  the  fittings  H.  These  tubes  are  connected 
to  the  glass  tubes  attached  to  Q  and  R  by  means  of  glass  to  metal  seals9  shown  at  Z'Z'. 
The  vertical  distance  between  the  ends  of  the  contact  points  T  and  U  is  accurately 
determined  by  means  of  a  cathetometer.  The  distance  through  which  the  displacement 
piston  S  moves  in  order  to  carry  the  mercury  in  Q  and  R  from  the  level  of  the  lower  point 
to  that  of  the  upper  point  is  accurately  determined  and  is  indicated  on  a  scale  5  placed 
alongside  the  piston.  This  scale  is  divided  into  32nds  of  an  inch  (0.8  mm.).  A  dial 
on  the  nut,  which  rotates  once  when  the  piston  moves  through  a  distance  equal  to  one 
scale  division,  is  divided  into  100  divisions,  and  this  serves  accordingly  to  divide  each 
Vs2  inch  into  100  parts.  Contact  between  the  platinum  points  and  the  mercury  in  the 
tubes  Q  and  R  is  indicated  by  means  of  a  telephone  receiver  placed  in  a  circuit  containing 
a  small  induction  coil.  This  arrangement  makes  possible  reading  pressure  differences 
with  a  precision  of  0.01  mm.  of  mercury. 

In  order  to  read  the  difference  in  the  level  of  the  mercury  surfaces  in  Q  and 
R,  the  following  procedure  is  carried  out.  Contact  is  first  made  with  the  lower 

9  Kraus,  U.  S.  pat.  1,046,084,  Dec.  3,  1912. 


19 

•contact  point  in  Q  and  the  reading  of  the  position  of  the  piston  5  is  noted  on  the  adja- 
cent scale.  Mercury  is  now  injected  or  withdrawn  from  Q,  and  R,  depending  upon 
whether  the  difference  in  pressure  is  less  or  greater  than  the  distance  between  the  points, 
until  the  upper  meniscus  makes  contact  with  the  point  in  R.  For  example,  to  obtain 
the  actual  value  of  the  difference  in  pressure  on  the  2  surfaces  when  this  is  less  than  the 
distance  between  the  2  points,  the  equivalent  height  of  mercury  injected  at  5"  is  sub- 
tracted from  the  distance  between  the  points.  When  the  difference  in  pressure  is  gi  eater 
than  that  between  the  points,  the  equivalent  height  of  mercury  withdrawn  is  added  to  the 
distance  between  these  points. 

Pressure  differences  greater  than  2  cm.  of  mercury  are  determined  by  reading 
directly  the  position  of  the  menisci  in  Q  and  R  by  means  of  a  cathetometer.  A  sheet  of 
polished  metal  placed  behind  the  meniscus,  with  strong  illumination  from  the  front,  gives 
a  very  sharply  defined  outline  of  the  meniscus  when  viewed  through  a  telescope.  Read- 
ings with  the  cathetometer  under  these  conditions  could  readily  be  reproduced  with  a 
difference  of  less  than  0.05  mm.  of  mercury. 

Valve  W  serves  to  separate  the  2  limbs  of  the  manometer  system,  Q  and  R,  when 
desired.  An  auxiliary  mercury  displacement  piston,  not  shown  in  the  figure,  is  connected 
at  X.  This  piston  has  a  capacity  approximately  4  times  that  of  5  and  is  employed  to 
adjust  the  surfaces  in  Q  and  R  to  any  desired  initial  point.  At  Y  is  shown  an  auxiliary 
manometer,  which  serves  to  indicate  the  relative  pressures  in  the  system  when  these 
pressure  differences  are  very  large,  as  they  often  are  when  ammonia  is  withdrawn  from 
the  tubes  containing  the  solution  or  the  pure  solvent. 

The  arrangement  for  introducing  ammonia  into  the  containers  will  be  described  in 
connection  with  the  experimental  procedure, 

Experimental  Procedure 

The  glass-lined  portions  of  the  containing  tubes  A  and  B  are  thoroughly  cleaned 
with  hot  chromic  acid  cleaning  mixture.  The  exposed  metal  portions  of  the  containers, 
the  internal  portions  of  the  valves,  and  the  metal  connections  are  washed  with  alcohol 
and  ether  and  wiped  clean  with  cotton.  The  tellurium,10  in  stick  form,  is  introduced  into 
the  glass-lined  tube  B  immediately  after  cleaning.  The  capsule  E,  containing  a  known 
quantity  of  sodium,  is  placed  in  position  as  shown  at  D,  and  B  is  closed  by  means  of  the 
screw  joint  G.  The  tubes  A  and  B  are  then  placed  in  position,  A  in  its  permanent  posi- 
tion in  the  thermostat  and  B  in  a  convenient  position  in  which  it  may  be  surrounded  with 
a  bath  of  liquid  ammonia.  Connections  to  the  flexible  copper  tubes  ZZ  are  then  made 
by  soldered  joints  X'X' '.  The  ammonia  is  contained  in  a  light  steel  cylinder  C'.  This 
ammonia  is  purified  by  distillation  into  C'  from  a  tank  in  which  it  has  previously  been 
purified  by  the  methods  described  by  Franklin  and  Kraus.11  C'  is  connected  to  a  valve 
Dr  by  means  of  a  length  of  flexible  copper  tube.  The  valve  D'  allows  of  connections 
being  made  with  the  vacuum  system,  when  desired.  A  second  flexible  tube  leads  from 
the  opposite  side  of  D '  to  the  valve  /.  This  arrangement  makes  possible  the  evacuation 
of  the  connecting  tubes  between  C'  and  either  container  A  or  B.  Such  an  arrangement 
was  found  necessary  when  it  was  desired  to  introduce  ammonia  into  A  or  B  without 
evacuating  the  entire  system. 

In  order  to  introduce  ammonia  into  the  container  A,  the  procedure  is  as 
follows.  C'  is  accurately  weighed  and  connected  to  D'  by  means  of  a  conical  compres- 
sion joint.  The  valve  /  is  opened  and  A ,  together  with  all  its  connections,  is  evacuated. 
When  the  pressure  has  fallen  to  a  few  thousandths  of  a  millimeter  of  mercury,  Valve  D ' 

10  The  tellurium  employed  in  this  investigation  was  prepared  in  connection  with  an 
earlier  investigation  in  this  Laboratory.     See  Kraus  and  Chiu,  Ref.  3. 

11  Franklin  and  Kraus,  Am.  Chem.  /.,  23,  284  (1900). 


20 

is  closed  and  the  valve  on  C'  is  opened.  The  cylinder  C'  rests  on  a  platform  balance  and 
is  surrounded  by  a  light  electrical  heater  of  tubular  form.  Approximately  the  desired 
quantity  of  ammonia  is  now  distilled  into  A  from  C'.  The  valve  I  is  then  closed,  C' 
is  disconnected  and  weighed,  and  thus  the  exact  amount  of  ammonia  introduced 
into  A  may  be  obtained. 

The  expanded  portions  of  A  and  B  have  a  capacity  of  approximately  100  cc.  About 
60  g.  of  ammonia  is  introduced  into  A  and  B.  About  V«  of  this  is  blown  into  water  con- 
tained in  a  lOOOcc.  flask,  the  exact  amount  of  ammonia  thus  removed  being  determined 
by  weighing  the  flask  before  and  after  the  absorption  of  ammonia  gas.  This  removal 
of  ammonia  was  found  necessary  in  order  to  insure  complete  elimination  of  foreign  gases 
from  the  system.  A  trace  of  foreign  gas  on  either  side  of  the  system  has  an  appreciable 
influence  on  the  pressure  difference  when  this  difference  reaches  a  value  of  a  few  milli- 
meters of  mercury. 

The  introduction  of  ammonia  into  B  is  carried  out  in  a  manner  similar  to  that  already 
described  in  the  case  of  A .  The  tube  B  is  outside  the  thermostat,  and  with  all  its  con- 
nections, including  Q,  is  thoroughly  evacuated  before  the  ammonia  is  introduced.  The 
lower  portion  of  B  is  then  introduced  into  a  bath  of  boiling  ammonia  contained  in  a 
Dewar  flask.  About  5  g.  of  ammonia  is  now  distilled  from  C'  into  B.  The  capsule  E 
containing  the  sodium  is  then  broken  and  allowed  to  drop  into  the  ammonia  in  the  con- 
tainer B.  This  container  is  then  shaken  for  a  period  of  30  minutes  in  order  to  facilitate 
the  initial  reaction  between  the  sodium  and  the  tellurium.  The  bath  of  liquid  ammonia 
in  the  Dewar  flask  is  then  removed  and  when  B  has  come  nearly  to  room  temperatures 
it  is  placed  in  position  in  the  thermostat  as  near  to  container  A  as  possible ;  55  g.  of  am- 
monia is  now  distilled  into  B  in  addition  to  that  already  introduced  and  about  */»  °f 
this  ammonia  is  blown  off,  as  has  already  been  described  in  connection  with  the  procedure 
in  filling  A.  This  then  gives  the  first  concentration  of  the  sodium- tellurium  complex, 
for  which  measurements  on  the  pressure  difference  are  carried  out.  After  having  deter- 
mined the  difference  in  pressure  between  the  solution  and  the  pure  solvent  at  this  con- 
centration, further  quantities  of  ammonia  are  removed,  the  amounts  being  accurately 
determined  by  absorption  in  water  and  weighing.  In  this  way  the  vapor  pressure  of  the 
solution,  relative  to  that  of  the  pure  solvent,  is  determined  at  a  series  of  concentrations. 
The  ammonia  present  in  the  container  at  the  last  concentration  is  determined  by  absorp- 
tion in  water  and  all  concentrations  are  calculated  back  from  this  value 

In  the  first  attempts  to  carry  out  the  reaction  between  the  sodium  and  the  tellurium 
in  B,  the  tube  B  was  placed  in  position  hi  the  thermostat  and  ammonia  was  condensed 
in  this  tube  at  the  temperature  of  the  thermostat,  18°.  Under  these  conditions,  it  was 
found  that  hydrogen  is  evolved  when  the  sodium  is  dropped  into  the  ammonia,  owing  to 
the  formation  of  sodium  amide.  As  a  result  it  was  found  impossible  to  determine  the 
true  vapor  pressure  of  the  solution.  In  order  to  overcome  this  difficulty,  the  reaction 
was  carried  out  at  the  temperature  of  boiling  liquid  ammonia,  as  has  just  been  described. 

It  is  necessary  to  correct  for  the  quantity  of  ammonia  present  as  vapor  above  the 
surface  of  the  liquid  and  in  the  various  connecting  tubes.  This  quantity  was  determined 
by  filling  the  apparatus  with  ammonia  vapor  under  the  pressure  existing  in  the  cylinder 
C'.  The  weight  of  this  ammonia  was  obtained  by  weighing  C'.  Knowing  the  mass  of 
ammonia  present,  the  temperature  and  pressure,  it  was  possible  to  calculate  the 
corrections  within  the  necessary  limits  of  precision.  In  applying  the  correction  at 
the  various  concentrations,  the  volume  of  liquid  ammonia  was  subtracted  from  the  total 
volume  of  the  apparatus  as  determined.  The  above  method  of  correction  is  not  entirely 
accurate;  but,  in  view  of  the  fact  that  the  correction  in  any  case  is  very  small,  it  was 
found  unnecessary  to  determine  the  correction  with  a  greater  degree  of  precision. 

After  the  completion  of  an  experiment  at  a  series  of  concentrations  with  a  given 
quantity  of  sodium,  ammonia  is  again  introduced  into  the  container  B,  which  still  con- 


21 

tains  the  sodium-tellurium  compound,  and  a  new  set  of  readings  is  made  at  a  series  of 
concentrations . 

The  amount  of  ammonia  in  the  container  A ,  about  30  g.  as  a  rule,  was  maintained 
constant  during  an  experiment. 

Experimental  Results 

The  results  of  all  experiments  carried  out  in  the  manner  described  are 
given  in  the  following  table.     At  the  head  of  each  sub-table  is  given  the 

TABI,R  I 
VAPOR-PRESSURE  LOWERING  OF  SOLUTIONS  OF  THE  COMPLEX  SODIUM  TELLURIDE  AT 

DIFFERENT  CONCENTRATIONS 
Liquid 
ammonia  Ratio 


X  10* 


G.  n  +  N  "  Mm.  Hg  P    '  P  '  n  +  N 

Series  1,  0.1113  g.  of  Na,   17.9° 

31.386  26.2  8.19  13.6  0.54 

21.186  38.8  12.54  20.9  0.54 

15.536  52.7  17.27  28.7  0.54 

10.261  79.8  26.05  43.2  0.54 

6.446  126.0  39.07  65.6  0.52 

Series  2,   0.055  g.  of  Na,    17.9° 

42.198  9.63  242  4.1  0.43 

13.582  29.9  10.25  17.0  0.56 

8.897  45.6  14.56  24.2  0.53 

Series  3,   0.055  g.  of  Na,    17.9° 

25.648  15.8  4.64  7.7      •  0.49 

17.348  23.4  7.35  12.2  0.52 

10.916  37.4  12.60  20.9  0.56 

Series  4,  0.055  g.  of  Na,   19° 

37.721        10.8        3.07       4.9  0.46 

27.166        15.0        5.16       8.28  0.55 

15.876        25.6        8.99       14.4  0.56 

10.366        39.1        14.28       22.9  0.58 

Series  5,  0.1398  g.  o?  Na,  19° 

40.041        25.8        7.60       12.2  0.47 

30.454        33.8        10.9        17.5  0.52 

19.384        53.0        17.2       27.7  0.52 

14.314        71.7       22.9       36.9  0.50 

9.154       112.0       35.9       57.7  0.51 

Series  6,  0.1398  g.  of  Na.  20° 

38.909  26.5  8.2  12.8  0.48 

28.767  359  12.0  18.7  0.52 

20.904  .        49.3  17.0  26.5  0.54 

15.272  67.3  22.8  35.5  0.53 

11.362  90.6  32.0  49.8  0.55 

number  of  the  series  of  the  experiment,  the  weight  of  sodium  employed 
in  the  series  in  question,  and  the  temperature  at  which  the  experiment  was 
carried  out.  In  the  first  column  is  given  the  weight  of  liquid  ammonia; 


22 

in  the  second  column,  the  value  of  the  molal  fraction,  n   \   pj  X  104;  in  the 

third  column,  the  pressure  difference,  AP,  in  millimeters  of  mercury ;  in  the 

AP 
fourth  column,  the  relative  pressure  difference,  -=-  X  104;  and  in  the  fifth 

AP,     n 
column,  the   ratio  ~p  / n   \   N' 

Discussion 

The  purpose  of  this  investigation  was  to  determine  the  complexity  of  the 
telluride  in  solution.  Since  even  the  binary  salts  are  relatively  slightly 
ionized  at  concentrations  in  the  neighborhood  of  0.1  N  and  since,  in  general, 
the  ionization  of  salts  of  higher  type  is  much  lower  than  that  of  typical 
binary  salts,  it  follows  that  the  ionization  process  of  the  dissolved  telluride 
might  be  expected  to  have  little  influence  on  the  observed  vapor-pressure 
change.  In  order  to  determine  the  complexity  of  the  telluride,  the  molecu- 
lar weight  of  the  dissolved  complex  must  be  determined.  It  is,  of  course, 
obvious  that  in  such  a  determination  the  true  molecular  weight  of  the  dis- 
solved compound  is  not  obtained  in  any  case,  but  merely  the  number  of 
moles  of  dissolved  substance  in  the  mixture.  If  the  laws  governing  dilute 
mixtures  hold,  then  the  number  of  moles  of  solute  for  any  given  composition 
of  the  mixture  may  obviously  be  determined  from  the  relative  vapor-pres- 
sure change  of  the  solution,  according  to  Raoult's  law.  Whether  or  not  the 
conditions  of  dilute  systems  are  fulfilled  in  solutions  of  electrolytes  at  a 
given  concentration  cannot  be  predetermined.  If,  however,  the  relative 
lowering  of  the  vapor  pressure  can  be  determined  at  a  series  of  concentra- 
tions, some  inference  may  be  drawn  as  to  whether  the  conditions  of  a  dilute 
system  are  fulfilled  in  a  given  case  from  the  manner  in  which  the  vapor 
pressure  varies  as  a  function  of  the  concentration  at  low  concentrations. 

AP  n 

If  Raoult's  law  holds,  then    obviously    -p-  =  — TT/u*     *n  other  words, 

the  ratio  -p-/ —      .,  equals  unity,  and  a  plot  of  the  observed  values  of 

AP/P  against  those  of  ^   ,   ^  should  yield  a  straight  line,  the  tangent  of 

whose  slope  is  unity.  If  the  laws  of  dilute  solutions  are  not  fulfilled,  then 
a  plot  of  the  values  of  AP/P  against  the  fractional  composition  will  lead 
to  a  curve  which,  at  sufficiently  low  concentrations,  where  the  deviations 
from  the  laws  of  dilute  solutions  become  small,  approaches  the  theoretical 
straight  line  asymptotically  From  vapor-pressure  determinations  at  a 
series  of  concentrations,  therefore,  it  is  possible  to  reach  a  conclusion  as  to 
whether  or  not  the  laws  of  dilute  solutions  are  fulfilled  within  the  limits  of 
experimental  error. 

In  the  preceding  table,  n  is  the  number  of  atoms  of  sodium  and  N  the 


23    ... 

number  of  moles  of  ammonia  in  the  mixture.     If  the  complex  telluride 
contained  only  a  single  atom  of  sodium  in  the  molecule,  the  value  of  the 

ratio  -p-/ — .    yy-  should  be  unity;  while,  if  2  atoms  of  sodium  were  present 
in  the  molecule,  the  ratio  should  have  a  value  of  0.5. 

In  Col.  5  of  the  table  are  given  the  values  of  the  ratio  -75- / — r~~/r>    f°r 

different  concentrations  of  the  solution.     An  inspection  of  the  table  will 

show  that  this  ratio  has  a  value  in  the  neighborhood  of  0.5.     In  Fig.  2 

\~p  A* 

the  values  of  —p  X  104  are  plotted  against  values  of  — ir~Tr  X  104.     While 

there  is  considerable  variation  among  the  various  points  due  to  errors  which 


104 


10   20   30   40   50   60   70   80  90   100  110  120 


10 
20 

30 
40 

§      50 
X 

K  60 
70 
80 


Fig.  2. — The  variation  of  the  vapor  pressure  of  the  sodium-telluride  solution 
as  a  function  of  composition. 

could  not  be  eliminated  entirely,  it  is  clear  that  the  points  determine  a 
curve  which  approaches  an  asymptote  for  which  -p/ — .  ^  has  a  value 

0.5.  The  straight  line  appearing  in  the  figure  represents  this  asymptote. 
In  the  more  dilute  solutions,  the  points  follow  this  theoretical  curve  within 
the  limits  of  the  experimental  error,  but  at  higher  concentrations  the  devi- 
ations from  this  curve  become  appreciable,  although  the  deviations  are 

nowhere  large.  The  mean  value  of  the  ratio  -p/ — r~iT7  is  0.52,  with 
a  maximum  variation  from  0.43  to  0.58.  The  higher  values  of  the  ratio 


24 

at  the  higher  concentrations  are  doubtless  in  part  due  to  deviations  from 
Raoult's  law,  while  at  lower  concentrations  they  are  probably  in  the  main 
due  to  experimental  errors.  At  the  lowest  concentrations,  the  total  volume 
occupied  by  the  solution  was  approximately  80  cc.,  under  which  conditions 
it  is  difficult  to  establish  equilibrium  between  the  liquid  and  the  vapor 
phase.  At  the  same  time,  at  these  concentrations,  the  total  pressure 
change  is  of  the  order  of  magnitude  of  3  mm.  On  the  whole,  the  results 
are  as  concordant  as  might  be  expected,  in  view  of  the  conditions  under 
which  the  experiments  were  carried  out.  The  lowest  concentration  is 
approximately  0.03  N.  The  results  show  conclusively  that  2  atoms  of 
sodium  are  present  per  molecule  of  the  complex  telluride  whose  composition, 
therefore,  is  represented  by  the  formula  Na2Te*,  where,  according  to  the 
measurements  of  Kraus  and  Chiu,  x  varies  from  3.8  at  concentration 
0.084  to  4.04  at  2.45. l2 

Since  the  number  of  atoms  of  sodium  present  in  the  molecule  corre- 
sponds with  that  of  the  normal  telluride,  Na2Te,  it  may  be  concluded  that 
the  valence  of  tellurium  in  the  complex  does  not  change,  when  the  com- 
plex is  formed.  The  complex  tellurium  ion,  therefore,  has  the  constitution, 
Te — Tey,  where  y  =  x—  1.  The  complex  telluride  ion  is  formed  by  the 
addition  of  tellurium  atoms  to  the  normal  telluride  ion.  Kraus  and  Chiu 
have  shown  that  at  least  2  complex  tellurides  exist  in  ammonia  solutions 
under  different  conditions.  In  a  solution  in  equilibrium  with  the  normal 
telluride,  the  composition  of  the  solution  corresponds  with  that  of  the 
compound  Na2Te2.  The  constitution  of  the  complex  anion  resulting  from 
this  compound,  therefore,  corresponds  with  the  formulaTe  Te.  In 
the  first  stage  of  complex  formation,  a  single  atom  of  tellurium  attaches 
itself  to  the  normal  telluride  ion.  In  the  final  solution  in  equilibrium  with 
metallic  tellurium,  a  number  of  complexes  may  be  present,  although  in 
view  of  the  fact  that  the  value  of  oc  under  these  conditions  approaches  very 
close  to  4.0  it  is  not  improbable  that  there  is  present  in  the  solution  the  ion 
Te--Te3. 

Since  the  valence  of  the  telluride  ion  in  the  complex  is  the  same  as  that 
of  the  normal  telluride,  the  valence  of  the  telluride  ion  does  not  change  on 
formation  of  the  complex.  This  has  an  important  bearing  on  our  concep- 
tions of  the  constitution  of  complex  ions  of  this  type.  As  has  already  been 
pointed  out,  other  of  the  less  electropositive  heavy  elements,  such  as  lead, 
tin  and  antimony,  form  complex  compounds  with  the  alkali  metals  which 
resemble  the  complex  tellurides  in  many  respects.  In  the  case  of  antimony, 
the  initial  compound  formed  is  Na3Sb  and  there  is  evidence  indicating  that 
the  initial  compound  formed  with  lead  is  Na4Pb.  In  the  case  of  the  latter 
element,  however,  the  normal  plumbide  is  not  stable  with  respect  to  the 
complex  and  free  metallic  sodium  in  solution,  decomposition  occurring  ac- 
12  The  concentration  is  expressed  in  atoms  of  sodium  per  liter  of  pure  ammonia. 


25   ' 

cording  to  a  reaction  of  the  type:  Na4?b  — >  Na  -+-  NaPb*.  In  the 
presence  of  excess  lead  the  ultimate  composition  of  the  solution  corresponds 
with  that  of  the  compound  Na4Pb.Pbs.  The  normal  plumbide  has  a 
constitution  corresponding  to  the  formula  Na4Pb,  and,  in  view  of  the  be- 
havior of  the  telluride  solutions,  it  may  be  inferred  that  the  valence  of 
the  plumbide  ion  remains  unchanged  in  the  complex.  On  the  other  hand, 
without  an  actual  determination  of  the  molecular  weight  of  the  plumbides 
in  solution,  it  cannot  be  definitely  stated  that  the  negative  valence  of  the 
plumbide  ion  may  not  vary  from  complex  to  complex.  It  is,  of  course, 
well  known  that  the  positive  valence  of  certain  elements,  such  as  lead,  for 
example,  varies  with  conditions;  and  it  is,  therefore,  conceivable  that  a 
similar  variation  may  occur  in  the  case  of  the  negative  valence  of  metallic 
elements.  It  appears  unlikely,  however,  that  a  change  of  the  negative 
valence  occurs  on  mere  addition  of  the  element  in  question. 

As  has  been  pointed  out  by  Kraus  in  an  earlier  paper,18  the 
results  obtained  from  a  study  of  the  various  complexes  in  liquid  am- 
monia, and  particularly  of  the  complex  tellurides,  have  an  important 
bearing  on  our  conceptions  as  to  the  nature  of  metallic  compounds.  In 
the  first  place,  there  is  clearly  brought  to  view  the  important  property  of 
elements,  in  general,  of  functioning  as  negative  ions.  This  property  is  com- 
mon to  the  typical  elements  of  the  seventh,  sixth,  fifth  and  fourth  groups, 
and  possibly  to  certain  elements  of  the  third.  That  is,  it  has  been  definitely 
shown  that  these  elements  form  complex  compounds  which  are  soluble 
in  liquid  ammonia  and  that,  in  solution,  the  more  electronegative  element 
is  associated  with  a  negative  charge.  In  order  to  account  for  the  properties 
of  metallic  compounds,  therefore,  we  must  take  into  account,  first,  the 
tendency  of  the  more  electronegative  elements  in  their  compounds  to  act 
as  negative  ions;  and,  second,  the  tendency  of  the  negative  ions  of  these 
elements  to  form  complex  ions  in  the  presence  of  larger  amounts  of  the 
same  elements.  The  electrochemical  properties  of  these  compounds  in 
ammonia  solution  clearly  show  that  in  solution  they  possess  all  the  proper- 
ties characteristic  of  electrolytes,  that  is,  of  salts ;  and  there  is  apparently 
nothing  to  differentiate  solutions  of  these  compounds  from  ordinary  salts 
in  the  same  solvent  under  similar  conditions.  These  compounds  in  solu- 
tion, therefore,  are  in  fact  salts.  In  solution  they  differ  from  other  salts 
with  which  we  are  familiar  only  in  that  the  negative  ion  is  complex  with 
its  composition  dependent  upon  conditions,  while  in  the  case  of  most  salts 
the  negative  ion  has  a  fixed  composition.  Nevertheless,  although  these 
compounds  are  true  electrocutes  or  salts  in  solution,  in  the  free  state,  they 
exhibit,  for  the  most  part,  characteristic  metallic  properties.  In  general, 
the  metallic  properties  of  these  compounds  are  the  more  pronounced,  the 
less  electronegative  the  negative  constituent,  and  the  less  electropositive 

13  Kraus,  /.  Am.  Chem.  Soc.,  44,  1216  (1922X 


26 

the  positive  constituent.  Thus,  the  normal  telluride  is  entirely  non- 
metallic,  while  the  normal  antimonide  is  a  metal.  So,  also,  the  sulfides  of 
the  alkali  metals  are  non-metallic  while  those  of  heavy  metals  are  metallic. 
The  lower  the  atomic  weight  of  the  electronegative  element  in  a  given 
group  of  elements,  the  less  pronounced  are  the  metallic  properties  of  its 
compounds.  Thus,  the  normal  phosphides  of  the  alkali  metals  are  non- 
metallic. 

It  should  be  noted,  also,  that  no  considerable  reaction  occurs  between 
the  solvent  and  the  metallic  compound  when  the  process  of  solution  takes 
place.  The  energy  effects  accompanying  solution  are  apparently  of  a  very 
low  order  of  magnitude,  thus  indicating  that  no  fundamental  reaction  oc- 
curs in  which  the  character  of  the  compound  in  solution  is  materially  altered 
from  that  in  the  solid  state.  It  may  be  inferred,  therefore,  that  metallic 
compounds  between  strongly  electropositive  elements,  such  as  the  alkali 
metals,  and  the  less  electropositive  elements  such  as  lead,  tin,  etc.,  have 
a  salt-like  structure;  that  is,  they  possess  an  ionic  constitution.  In  this 
way  it  is  possible  to  account  for  many  of  the  properties  of  metallic  com- 
pounds which  otherwise  cannot  readily  be  reconciled  with  present  concep- 
tions as  to  the  constitution  of  elementary  substances. 

One  of  the  striking  features  of  the  interaction  between  a  given  pair  of 
metallic  elements  is  the  large  number  of  compounds  derivable  from  a  single 
such  pair  of  elements.  Such  compounds  cannot  be  accounted  for  on  the 
basis  of  any  of  the  accepted  theories  of  valence  or  of  atomic  structure. 
Taking  into  account,  however,  the  tendency  of  the  less  electropositive 
metallic  elements  to  form  negative  ions  and,  furthermore,  the  tendency  of 
these  ions  to  form  complexes,  compounds  of  this  type  are  readily  accounted 
for  and  may  be  harmonized  with  present  views  of  atomic  structure.  Every 
element,  thus,  has  an  electropositive,  as  well  as  an  electronegative  valence. 
The  negative  valence  is  one  for  the  seventh  group  of  elements  and  in- 
creases by  one  in  passing  to  an  adjacent  group  from  left  to  right,  just  as 
the  positive  valence  increases  in  passing  from  group  to  group  from  right 
to  left  in  the  periodic  table.  The  negative,  as  also  the  positive,  valence  is 
4  for  the  fourth  group  of  elements.  Whether  or  not  the  negative  valences 
may  increase  above  4  cannot  be  stated.  The  chief  distinction  between 
electronegative  and  electropositive  valence,  aside  from  the  sign  of  the 
charge,  is  that  the  ions  carrying  a  negative  charge  have  a  great  tendency 
to  form  definite  complexes  with  other  atoms.  The  nature  of  the  combi- 
nation, in  this  case,  is,  at  present,  not  understood.  Nevertheless,  we  are 
dealing  here  with  a  phenomenon  which  is  in  no  sense  restricted  to  a  small 
group  of  elements. 

While  the  only  metallic  compounds  whose  constitution  can  be  arrived 
at  are  those  which  are  soluble  in  liquid  ammonia,  it  does  not  follow  that 
such  an  ionic  constitution  is  restricted  to  compounds  which  are  soluble. 


27 

It  is  possible,  and  indeed  probable,  that  many,  if  not  all,  metallic  com- 
pounds are  of  this  type,  the  more  electropositive  constituent  being  present 
as  a  positive  ion  and  the  more  electronegative  constituent  as  a  negative 
ion.  In  these  compounds  the  electronegative  constituent,  at  any  rate, 
may  be  present  in  the  form  of  a  complex  ion.  Whether  the  positive  con- 
stituent may  likewise  form  a  complex  ion  under  suitable  conditions  cannot 
now  be  stated. 

In  the  past  the  term  "salt"  has  been  restricted  to  non-metallic  compounds 
having  ionic  constitution,  namely,  compounds  exhibiting  ionic  properties 
in  solution  and  in  the  pure  state  and  showing  no  metallic  properties. 
Metallic  compounds,  on  the  other  hand,  have  practically  not  been  classi- 
fied, and,  for  the  most  part,  have  been  sharply  differentiated  from  the  salts. 
According  to  the  views  here  proposed,  there  is  no  sharp  line  of  demarcation 
between  the  salts  and  metallic  compounds.  The  property  of  metallicity 
is  a  more  or  less  accidental  one,  depending,  of  course,  upon  the  nature  of 
the  elements  present  in  the  compound,  and  particularly  upon  the  relative 
electropositiveness  and  electronegativeness  of  the  constituents.  In  other 
respects,  however,  there  is  nothing  to  indicate  any  marked  break  in  the 
physical  and  chemical  properties  of  binary  compounds  between  two  ele- 
ments, as  we  pass  from  ordinary  salts  to  true  metallic  compounds.  If 
one  constituent  is  strongly  electropositive  and  the  other  constituent 
strongly  electronegative,  then  the  resulting  compound  is  a  typical  salt  which 
shows  no  metallic  properties.  As,  however,  the  electropositiveness  of  one 
constituent  and  the  electronegativeness  of  another  constituent  becomes 
less  pronounced,  the  metallic  characteristics  become  more  accentuated 
and  the  resulting  compounds  exhibit  metallic  properties,  except  in  the  case 
of  elements  which  are  relatively  very  strongly  electronegative  and  electro- 
positive. Thus,  practically  all  the  compounds  of  the  halogens  with  other 
elements  are  either  salt-like  or  neutral  substances.  It  is  only  seldom  that 
they  show  metallic  properties.14 

In  the  case  of  elements  of  the  sulfur  group,  the  normal  compounds  with 
the  alkali  metals  appear  throughout  to  be  non-metallic.  Certain  of  the 
complex  compounds,  however,  such  as  the  tellurides,  exhibit  metallic 
properties  even  in  the  case  of  the  alkali  metals,  as  has  already  been  noted. 
On  the  other  hand,  even  the  normal  tellurides  of  the  less  electropositive 
elements,  such  as  silver  and  lead,  exhibit  distinctly  metallic  properties. 
Indeed,  we  are  not  confined,  here,  to  the  tellurides;  as  is  well  known,  the 

14  It  is  interesting  to  note  in  this  connection  that  cuprous  iodide  is  a  typical  salt-like 
substance,  exhibiting  purely  non-metallic  properties  in  the  pure  state.  It  absorbs 
iodine  in  the  solid  state,  however,  yielding  a  substance  exhibiting  metallic  properties 
which  are  a  function  of  the  amount  of  iodine  absorbed.  The  greater  the  amount  of 
iodine  present  in  this  system,  the  more  do  the  properties  resemble  those  of  characteristic 
metallic  substances.  [Baedeker,  Ann.  Physik,  22,  765  (1907);  29,  566  (1909). 
Baedeker  and  Pauli,  Physik,  Z.,  9,  431  (1908).] 


28 

normal  sulfides  and  even  the  oxides  of  many  elements  exhibit  metallic 
properties  in  certain  states  as,  for  example,  some  of  the  iron  oxides  and 
some  of  the  natural  sulfides  of  lead.  There  is  nothing  to  indicate  that, 
in  their  constitution,  these  metallic  compounds  differ  materially  from 
similar  non-metallic  compounds  which  exhibit  a  salt-like  structure.  The 
structure  of  all  such  compounds,  therefore,  is  essentially  of  the  same  type, 
corresponding  to  that  of  normal  salts,  while  the  metallic  properties  are 
determined  primarily  by  the  relative  electropositiveness  and  electro- 
negativeness  of  the  elements  concerned  in  the  compound.  Metallic 
compounds  should,  therefore,  be  classed  with  the  salts. 

Summary 

1.  The  vapor  pressure  lowering  due  to  the  complex  sodium-tellurium 
compound  in  liquid  ammonia  has  been  measured  at  a  series  of  concentra- 
tions down  to  0.03  N. 

2.  When  the  values  of   AP/P  are  plotted    against  values  of  ,,» 

where  n  is  the  number  of  atoms  of  sodium  in  the  mixture,  a  curve  results 
which  in  dilute  solution  approaches  very  closely  to  a  straight  line,  for 

A  P         vt 

which  the  value  of  -p/      .   ^  equals  0.5.     Apparently  Raoult's  law  is 

very  nearly  obeyed  by  solutions  of  the  complex  telluride  in  liquid  ammonia, 
and  from  the  value  of  the  above  ratio  it  follows  that  2  atoms  of  sodium  are 
present  per  molecule  of  the  complex  telluride  present  in  solution.  The 
complex  telluride  ion,  therefore,  carries  2  charges.  The  formation  of  the 
complex  telluride  consists  in  the  addition  of  tellurium  atoms  to  the  normal 
telluride  ion,  the  valence  of  the  telluride  ion  undergoing  no  change  under 
these  conditions. 

3.  The  bearing  of  this  result  on  our  conceptions  of  the  nature  of  other 
similar  complexes  in  ammonia  solution  and  of  metallic  alloys  in  general  is 
discussed. 


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